Public-address system



Aug. -25, 1925. 1,550,724

, F. A. HUBBARD PUBLIC ADDRESS SYSTEM Filed March 23. "1922 A, x *1??? V1 Y Patented Aug. 25 1.925?

UNETED STATES FRANCIS A. HUBBARD, OF VIEST ENGLEVOOD, NEW JERSEY,ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, 015' NEW YORK, N.Y., A CORPORATION OF NEW YORK.

PUBLIC-ADDRESS SYSTEM.

Application filed March 23, 1922.

To all whom it may concern:

Be it known that I, FnANoIs A. HUBBARD, a citizen of the United States,residing at West Englewood, in the county of Bergen. State of NewJersey, have invented certain new and useful Improvements in Public-Address Systems, of which the following is a full, clear, concise, andexact description.

This invention relates to electrical systems for the transmission ofsound and particularly to those employing a plurality of loud speakerprojectors for use in addressing or in entertaining audiences.

If loud speaking systems employing a plurality of loud speakingprojectors were always used under ideal climatic and acousticalconditions, the projectors could advantageously be adjusted to the samevolume. Although substantially ideal con ditions may be provided so faras a speakers voice is concerned, difiiculties are encountered when hisvoice is highly magnified and distributed in all directions by loudspeaker systems. Sound reflecting surfaces and objects ordinarily out ofthe speakers voice range may be well within the projectors range andunless means are provided to control the volumes of the projectors,echoes and other interferences will result and materially interfere withthe intelligibility and the proper distribution of the sound. This istrue for both indoors and outdoors speaking.

It is also desirable to be able to control the volumes of the variousprojectors to compensate for the poor acoustics usually found in certainsections of auditoriums; and when the system is used outdoors tocompensate for the direction and velocity of the wind. While it isdesirable to adjust the projectors to give uniform distributionobviously in many cases this cannot be conviently accomplished. It is,therefore, necessary to adapt a loud speaking system to the surroundingconditions in order to produce satisfactory results.

An object of the invention is to provide a public address system with aneflicient means for regulating the power delivered tothe projectors.

Serial No. 545,993.

Another object is to provide a public address system having a pluralityof loud speaking projectors, the volumes of which may be varied inaccordance with the climatic and acoustical conditions within the rangeof the projectors.

Other objects will appear hereinafter.

In general the invention comprises atransmitter connected to apluralityof loud speaking projectors through a multi-tap transformer forselectively and severally controlling the volumes of the projectors.

In the drawing, Fig. 1 represents schematically a loud speaker systemembodying the invention.

Fig. 2 is a plan view of the projectors as installed.

Fig. 3 is an elevation of the arrangement shown in Fig. 2.

A high quality transmitter 4 is connected to the primary of atransformer 7 The transmitter 4 is preferably of the pushpull typedisclosed in an application of G. R. Lum for Letters Patent Serial No.570,970, filed June 26, 1922, which discloses a push-pull transmitterair damped in the manner shown in patent No. 1,456,588 of May 29, 1923to I. B. Crandall. The diaphragm, or the common electrode, of thetransmitter, is connected through a battery 5 and an adjustableresistance 6 to the neutral or central point of the primary, and theother electrodes are connected to the opposite ends. The secondary ofthe transformer is connected to the input of amplifiers 8 and 9 of anamplifying circuit such as disclosed in Patent No. 1,128,292, ofFebruary 16, 1915, to E. H. Golpitts, and the output circuit isconnected to the primary of transformer 10, and the secondary oftransformer 10 to an auto-transformer 11 having a plurality of tapswhich are connected to multi-point switches 13. One side of eachprojector 12 may be connected in common to one end of transformer 11,and the other side of each projector to a rotating arm 14 on the switch13. With this arrangement, the power delivered to each projector may beaccurately controlled with the minimum loss of energy and with efficienttransformers the energy loss between the output terminals of theamplifier and the projectors is negligible. Although the drawing showsan auto-transformer, it is obvious that the secondary of transformer 10may be provided with taps and the auto-transformer omitted, and undercertain conditions thi may be the preferable arrangement. It should benoted in this connection that the output transformer 10 has two parallelprimary windings and two parallel secondary windings with a common core,the second ary windings being superimposed upon the primary windings.

The projectors consist preferably of re ceivers of the type disclosed inPatent No. 1,365,890, January 18, 1921 to H. C. Egerton, equipped withsuitable horns.

In an installation for reinforcing a speakers voice and extending itsrange, the projectors may be arranged in a horizontal plane above thespeaker, but are usually adjusted so as to be slightly lower at theiropen ends than at their receiver ends. The receiver ends are usuallydisposed as near as practical at the same point, the horns projectingradially therefrom. The center of the grou of projectors issubstantially above the speaker. The transmitter, or transmitters, as itmay be desirable to use more than one in order to give the speaker morefreedom, are located at any convenient place within the acousticalshadow of the projectors, that is, the region within the neighborhood ofthe projectors where the sound therefrom is substantially inaudible.This arrangement of the sound projectors and transmitter forms no partof the present invention, but it is disclosed and claimed in Gr. D.Edwards application, Serial No. 560,507, filed May 12, 1922. Such anarrangement is important to prevent interference or howling between thetransmitter and the projectors.

The invention also provides a convenient arrangement for eliminatingtransition losses. It is the practice to construct amplifiers to operatemost efficiently on a fixed impedance load. For any other loads,therefore, a certain amount of energy is wasted, and in some cases, theenergy so wasted in addition to the useful energy, would require alarger size amplifier. By providing a multi-tap transformer, and meansfor selectively and severally controlling the energy delivered to theloud speakers, the difference in the impedances of the amplifier and theload may be readily corrected by raising or dropping each receiver tap agiven amount.

Figs. 2 and 3 represent schematically the relation of the speaker, theprojectors, and the transmitter. The actual arrangement of theprojectors, as well as their volumes, is dependent upon the distributionof the audience, and the acoustical characteristics of the surroundings.In the case of long distance transmission the audience depends entirelyupon the projectors. In this case the projectors may be grouped asalready described.

The invention claimed is:

l. A public address system comprising a plurality of loud speakingprojectors, a voltage regulator common to said projectors and switchingmeans individual to said projectors for selectively and severallycontrolling the volumes thereof, by altering the association of saidcommon voltage regulator and said projectors.

2. A public address system comprising a transmitter, a plurality of loudspeaking projectors a multi-tap transformer common to said projectorsand switching means inclividual to said projectors for selectively andseverally controlling the volumes thereof.

3. A public address system comprising a transmitter, a plurality of loudspeaker projectors in parallel, a multi-tap transformer common to saidprojectors and switching means individual to said projectors forselectively and severally controlling the volumes thereof.

4. A public address system comprising a transmitter, a plurality of loudspeaking projectors in parallel, a multi-tap transformer common to saidprojectors, and a plurality of multi-point switches connecting saidprojectors to said transformer.

A public address system comprising a transmitter, amplifiers, aplurality of loud speaking projectors, a multi-tap transformer common tosaid projectors, and switching means for selectively and severallycontrolling the volumes of said projectors.

6. A public address system comprising a transmitter substantiallyequally responsive to all voice frequencies for converting sound wavesinto electrical variations, substantially distortionless amplifiers foramplifying said electrical variations, a plurality of loud speakingprojectors for translating the amplified electrical variations intosounds, a transformer common to said projectors and switching means forselectively and severally controlling the volumes of said projectors.

7. A public address system comprising a transmitter substantiallyequally responsive to all voice frequencies for converting sound wavesinto electrical variations, substantially distortionless amplifiers foramplifying said electrical variations, a plurality of loud speakingprojectors in parallel, for translating the amplified electricalvariations into sounds. a multi-tap transformer common to all projectorsand a plurality of switches connecting said projectors to saidtransformer taps for selectively and severally varying the voltagesacross the pro jectors.

8. In an electrical system for the transmission of sound, a transmittersubstantially equally responsive to all sound Waves, substantiallydistortionless amplifiers, a plurality of loud speaking projectors, atransformer having its primary connected to said amplifiers, a voltageregulator common to all projectors connected to the secondary of saidtransformer, multi-point switches for said projectors said switchesconnected 10 in parallel to said regulator.

In Witness whereof, I hereunto subscribe my name this 17th day of MarchA. D., 1922.

FRANCIS A. HUBBARD.

